Display screen or portion thereof with transitional graphical user interface



FIG. 1 is the first image in a sequence of a display screen or portion thereof with transitional graphical user interface showing my new design;

FIG. 2 is the second image thereof;

FIG. 3 is the third image thereof; and,

FIG. 4 is the fourth image thereof.

The dashed broken lines around the figures show a display screen or portion thereof and form no part of the claimed design.

The dashed broken lines within the figures show unclaimed portions of the graphical user interface and form no part of the claimed design.

The subject matter in this patent includes a process or period in which an image changes into another image. This process or period forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 